1. Field of the Invention
The present invention relates to a multiphoton-excitation-type examination apparatus.
2. Description of Related Art
One example of a conventional apparatus for observing the function of cells and the like by irradiating a biological specimen with excitation light from the surface thereof and detecting the fluorescence produced from a comparatively deep location below the surface of the specimen is a multiphoton-excitation-type microscope (for example, see Japanese Unexamined Patent Application Publication No. 2002-243641, page 3 etc.).
This multiphoton-excitation-type microscope uses an ultrashort pulsed laser as a laser light source to emit ultrashort pulses. It is known that the pulse width of ultrashort laser pulses increases due to group velocity dispersion upon passing through optical components, such as optical fibers, lenses in optical devices, and the like.
Accordingly, a technique has been disclosed in which a so-called pulse stretcher, composed of a prism, is disposed at the input face of an optical fiber to lengthen the pulse width, so that the pulses are introduced into the optical fiber with the peak power of each pulse reduced, and a pulse compressor is disposed at the output face of the optical fiber to introduce the light to an optical device after compressing the pulse length to at least the length when the laser light was emitted. By doing so, when the light is irradiated onto a specimen from an objective lens, the pulse width can be made close to the original pulse width of the laser light.
However, the measurement head, which irradiates the specimen with laser light and detects fluorescence or reflected light obtained therefrom, should be made more compact from the viewpoint of the need to carry out measurement from any angle and position with respect to the examination site in a small laboratory animal or the like. Accordingly, the structure disclosed in Japanese Unexamined Patent Application Publication No. 2002-243641 suffers from the drawback that it is not possible to reduce the size of the measurement head. Also, if it is necessary to use different optical systems depending on the measurement site, the need for a small measurement head that can be exchanged should be considered. In such a case, since a pulse stretcher and pulse compressor are disposed outside the measurement head, as in the conventional art, there is a drawback in that adjustment of the pulse stretcher and pulse compressor must be carried out each time the measurement head is exchanged. Also, since the pulse stretcher and pulse compressor are disposed outside the laser light source, the optical fiber, and the measurement head, as in the conventional art, there is another drawback in that the overall size of the apparatus becomes large.